History and important experiments Flashcards
What was Griffith’s experiment in 1928? What did he conclude? What concept did it show?
He had two strains of Streptococcus pneumonia, R and S. The S strain was virulent and the R strain was completely harmless. When he injected a mouse with the S strain bacteria, it died. When injected with the R strain, the mouse lived. When injected with heat killed S strain bacteria, the mouse lived. When injected with heat killed S cells and living R cells, the mouse died. He concluded that the S cells had something not destroyed by heat, that the R cells took up to become virulent. Demonstrated transformation
What was Avery, Macleod, and McCarty’s experiment in 1944? What did they conclude?
They had repeated Griffith’s experiment, but removes either DNA, RNA, or proteins via enzymes. They then mixed the heat killed S cells with one of the three things removed with live R cells and watched if the mouse died. Transformation occurred and the mouse died when RNA and proteins were removed, but not when DNA was removed. They concluded that DNA must be the hereditary material
Why did scientists still believe protein was the hereditary material after Avery, Macleod, and McCarty?
Protein was far more complex than DNA, and humans couldn’t possibly share the same molecule of genetic material as bacteria
What was Hershey and Chase’s experiment in 1952? What did they conclude?
They used bacteriophages and radioactive isotopes to determine the location of the protein and the DNA following centrifugation. Radioactive phosphorus was used to label DNA and radioactive sulfur was used to label proteins. The bacteria were infected with labelled viruses, then the viral parts were separated with centrifugation. They found the proteins were in the supernatant and the DNA was in the pellet with the bacterial cells. They concluded that DNA was the hereditary material
What was Chargaff’s experiment? What did he find?
He had lysed cells, treated them with protease, then acid to separate individual nucleotides. He separated the nucleotides with chromatography, then put them back into solution and measured the quantity of each one with a spectrophotometer. He did this for many different species and found that all DNA was made of the same 4 bases, and that each species had a specific ratio of each one. The ratio wasn’t 1:1:1:1, nor was it completely random
How did Rosalind Franklin indirectly observe the structure of DNA?
X-ray crystallography. Saw a distinct x shape that was from a diffraction image of DNA.
What was the Messelson-Stahl experiment? What did they conclude?
Used heavy and light isotopes of nitrogen to determine if DNA replication followed the conservative, semi-conservative, or dispersive model. They used a CsCl density gradient which makes the heavier isotope form a band closer to the bottom and the lighter isotope forms a band on the top. They concluded the semi-conservative model was the right one
What were the observations of Archibald Garrod in 1908? What did he conclude from that?
He showed that human disease can be hereditary, and that many hereditary diseases are from problems in biochemical processes. Concluded that genes encoded proteins, and that human disease had a genetic root
What was Beadle and Tatum’s experiment? What did it show?
Mutated Neurospora fungus, transferred spores to a complete medium and let them grow. Then transferred to minimal media and observed that some couldn’t grow until methionine was added to the plate. Showed that mutations alter specific steps in biochemical pathways, one gene one enzyme
What was Boveri and Sutton’s theory?
Chromosome theory of heredity. The genetic material responsible for heredity was found in chromosomes
What was Thomas Morgan’s experiment? What did he conclude?
He studied eye colour in Drosophila (also the first to use Drosophila for genetic research). When he crossed a red eyed female to a white eyed male, he was expected all the progeny to have red eyes in F1, and 3 red to 1 white in F2. Instead, he saw that all the females and half the males had red eyes in the F2, and the other half of the males had white eyes. From this, he concluded that some traits are linked to sex, and they are carried on the sex chromosomes
